Personal computers, workstations, servers and the like usually take the form of a single system unit having access areas in one or more sides for switches, storage media and network, peripheral or power connectors. While it is common to fabricate system unit enclosures from sheet metal, design aspects of such enclosures vary widely due to competing constraints imposed by various goals.
One goal of computer enclosure design is to minimize the volume occupied by the system unit while conserving space inside the enclosure for internal system components. Another goal is to provide ample structural support and fastening surfaces for internal system components. Another goal is for the enclosure to prevent electromagnetic energy from escaping from the system unit and causing electromagnetic interference ("EMI") with other systems or devices. Yet another goal is to prevent fluid from escaping the system unit enclosure in the unlikely event of a component failure that involves melting or leakage. (One of the certification tests performed by United Laboratories, Inc. on computer system units is to pour flaming oil into the enclosure and determine whether the enclosure is able to contain the oil within the volume of the system unit. To be commercially successful, an enclosure design must be able to pass this United Laboratories "flaming oil" test.)
Additionally, a good design should be aesthetically pleasing. In this regard, it is usually considered desirable for a system unit to appear free of fasteners and fastener-related blemishes when viewed from the outside. To accomplish this look, prior art system unit enclosures have been fitted with metal or plastic outer covers, the purpose of which is entirely cosmetic--to hide enclosure fasteners such as rivets, welds and screws. But such a solution adds to the weight, expense and complexity of the enclosure. Another prior art solution to this problem has been to use spot welding on the inside of the enclosure. Even spot welds, however, are slightly visible when viewed from the outer side of the sheet metal. While it is possible to diminish the visibility of spot welds if thicker sheet metal is used for the enclosure, thicker sheet metal adds undesirable weight and cost to the system unit. A technique known as TOX riveting has also been used to construct computer enclosures. (TOX is a trademark of TOX Systems, Pty. Ltd., Melbourne, Australia.) But TOX riveting, by design, leaves a notable indentation on one side of the riveted pieces and a raised bump on the other side.
It is therefore an object of the invention to provide a computer enclosure that is free of fastener-related blemishes when viewed from the outside.
It is a further object of the invention to avoid adding weight or cost to the enclosure relative to the weight and cost of the enclosures of the prior art.
It is a further object of the invention to conserve volume that may be used for mounting internal system components.
It is a further object of the invention to provide ample structural support and mounting surfaces for internal system components.
It is yet a further object of the invention to achieve all of the above objectives in a manner that is consistent with ease of manufacturing.